The 34-year-old wore prosthetics and padding after TV bosses had her character Betty put on weight for a storyline in an effort to hide the actress' real life pregnancy.
Recalling the first time she saw herself on screen, she said: 'I saw it on the air, paused it and went screaming into the other room.'
Scroll down for video....
Mad women: January Jones told the Hollywood
Reporter that she ran screaming from the room after seeing herself as
'fat Betty' on screen
In an interview with The Hollywood Reporter, she said she came to 'love' the fat suit while filming. 'I got used to it,' said the single star, who welcomed her son Xander in September.
She continued: 'I started this season of Mad Men eight months pregnant, and I finished it with a 5-month-old. It was bizarre.
'And I was in seven hours of prosthetics every morning, trying to rip off a fake chest piece so I could breastfeed. [...] I loved [the fat suit]. I didn't want to try to hide it, I thought it would become comical and weird.
Battle of the bulge': January's Mad Men character struggles with her weight and is even seen eating whipped cream from a can
In the show, 'Fat Betty' struggles to lose the pounds gained as a result of being a bored and depressed housewife and joins Weight Watchers in an effort to get back in shape.
Jones appears in the magazine alongside fellow actresses Claire Danes, Mireille Enos, Julianna Margulies, Emmy Rossum and Kyra Sedgwick, who all posed for a glamorous photoshoot and discuss the ups and downs of the job.
Leading ladies: The actresses posed in glamorous gowns for the shoot in
downtown Los Angeles, from left Julianna Margulies, Emmy Rossum, Claire
Danes, January Jones, Mireille Enos and Kyra Sedgwick
Primetime's leading ladies shared some of their most embarrassing and scary professional moments with the magazine in the upcoming issue and participated in a roundtable video discussion.
Wearing a slinky white dress with beaded sleeves and detailing at the neck, Jones also revealed that she had nearly quit acting after a particularly embarrassing audition.
'It was an audition for Coyote Ugly, my second audition ever,' she recounted, 'They said, You're going to dance to Prince's 'Kiss.' You're going to pole dance, but there is no pole. And I just turned beet red. It was awful.'
Shameless: Emmy Rossum is contractually obliged to show 'side-boob' on her TV show
The Closer: Kyra Sedgewick admitted that she auditioned for Flashdance in a tiny mini-skirt and heels
Drama lesson: Six leading actresses featured on the Emmy Kick Off issue alongside January Jones
Shameless actress Emmy Rossum also opened up about her nude scenes on the show.
'I thought it suited the character,' she said. 'This is a very low-income family, they have very thin walls, they don't have money for entertainment, and this girl likes to have sex.
For me to glamify her would be not realistic'.
Rossum revealed that the contract she had signed included clauses like: 'You will show partial side boob, you will show two cheeks …'
The 25-year-old singer added: 'When I got on set -- I'd never done nudity before -- I was like, Oh, everyone here is human.'
But she admitted: 'Some days you feel like, Oh, God. I wish we were shooting this last week, I felt so skinny.'
When asked about the most terrifying things they had ever had to do on screen, Canadian actress Mireille Enos, star of The Killing, said: 'Is it wrong to admit that having to kiss Brad Pitt was very, very terrifying?
'It was on World War Z, which I shot last summer and it was the second day of shooting.
My so-called life: Clare Danes talked about the pressures of shooting a TV series with her fellow actresses
The Good Wife: Julianna Margulies admitted that she struggles to find time for her family
The stars also discussed stage fright and forgetting their lines in the story which was shot on a rooftop in downtown Los Angeles.
The deadline for Emmy nominations is at the end of June with the Primetime Emmy® Awards, which celebrate excellence in national primetime programming, airing in September.
The Emmy Kick Off issue of the Hollywood Reporter is on newsstands now.
Terrifying: Never mind serial killers, Mireille Enos was scared when she had to kiss Brad Pitt in a recent film